Modern drug development has shown that the market for injectable drugs is growing, since the majority of these molecules are too large and fragile to be delivered by other methods such as orally. However, it is difficult to formulate many of these molecules into stable solutions that are sufficiently concentrated to inject an efficacious amount in a reasonable sized dose (<1 ml). As a result, the formulation may be quite viscous, often up to 10,000 times thicker than water i.e. 10,000cS (centistokes) or higher. Also, the advent of controlled release strategies has opened new areas for development and delivery of formulations. For parenteral applications, the viscosity of enhanced formulations has been an issue with several controlled release formulations. Liquids with viscosities significantly higher than water become increasingly difficult, if not impractical, to inject as viscosity increases using a conventional needle and syringe.
Viscous formulations containing polymers, for example, are employed for the controlled release of drugs after Intra-venous (IV) subcutaneous (SC), intra-dermal (ID) or intra-muscular (IM) injection. These formulations are notoriously difficult to inject, requiring a large force to be delivered by the hand of the care-giver, and often quite painful for the patient. The force required for injection is associated with viscous drag of the formulation while traversing the length of the needle. Consequently, large bore needles are employed (creating even greater levels of pain), but still the injection time can be in the order of minutes or more.
The ability to inject a drug incorporated into a polymer to a localized site and have the polymer form a semi-solid drug depot has a number of advantages. Among these advantages is ease of application localized delivery, prolonged drug delivery, and better compliance with prescribed therapy due to less frequent dosing. The better compliance is very important for delivery of psychiatric drugs, wherein the disease state can make compliance difficult or impossible, and a depot can allow for infrequent, e.g. monthly, dosing in a clinical setting. For these reasons a large number of in situ setting polymeric delivery systems have been developed and investigated for use in delivering a wide variety of drugs.
Currently, there are few synthetic or natural polymeric materials which can be used for the controlled delivery of drugs, including peptide and protein drugs, because of the strict regulatory compliance requirements, such as biocompatibility, clearly defined degradation pathway, and safety of the degradation products. The most widely investigated and advanced biodegradable polymers in regard to available toxicological and clinical data are the aliphatic poly(.alpha.-hydroxy acids), such as poly(D,L- or L-lactic acid) (PLA) and poly(glycolic acid) (PGA) and their copolymers (PLGA). These polymers are commercially available and are presently being used in medical products, for example as bioresorbable sutures. An FDA-approved system for controlled release of leuprolide acetate, the Lupron Depot.™, is also based on PLGA copolymers. The Lupron Depot., consists of injectable microspheres, which release leuprolide acetate over a prolonged period (e.g., about days) for the treatment of prostate cancer.
A. S. Sawhney and J. A. Hubbell, J. Biomed. Mat. Res., 24, 1197-1411 (1990), synthesized terpolymers of D,L-lactide, glycolide and c-caprolactone which degrade rapidly in vitro. The hydrophilicity of the material was increased by copolymerization with a poloxamer surfactant (Pluronic F-68). This poloxamer is a block copolymer comprising about 80% by weight of a relatively hydrophobic poly(oxypropylene) block and 20% by weight of a hydrophilic poly(oxyethylene) block. Copolymerization with the poloxamer resulted in a stronger and partly crystalline material which was mechanically stable at physiological temperatures (e.g. 37.degree. C.) in water.
One system, which can be fabricated in aqueous solution, is a class of block copolymers referenced above and marketed under the Pluronic™ tradename. These copolymers are composed of two different polymer blocks, i.e. hydrophilic poly(oxyethylene) blocks and hydrophobic poly(oxypropylene) blocks to make up a triblock of poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene). The triblock copolymers absorb water to form gels which exhibit reverse thermal gelation behavior.
Churchill et al, U.S. Pat. Nos. 4,526,938 and 4,745,160 show copolymers that are either self-dispersible or can be made self-dispersible in aqueous solutions. These copolymers are ABA triblock or AB block copolymers composed of hydrophobic A-blocks, such as polylactide (PLA) or poly(lactide-co-glycolide)(PLGA), and hydrophilic B-blocks, such as polyethylene glycol (PEG) or polyvinyl pyrrolidone.
Dunn et al, in U.S. Pat. No. 5,324,519, disclose the composition of a liquid formulation of a thermoplastic polymer and a pharmaceutically acceptable organic solvent (trade name Atrigel). The composition is administered as a liquid to an implant site, whereupon the solvent diffuses or dissipates into the surrounding aqueous tissue fluids. The thermoplastic polymer is not soluble in these aqueous fluids so that it coagulates or solidifies to form a microporous solid or gelatinous matrix. The composition is a liquid formulation of a thermoset prepolymer or copolymer, preferably an acrylic ester-terminated biodegradable prepolymer, which is capable of cross-linking in situ to form a polymeric or copolymeric solid or gelatinous matrix.
In U.S. Pat. No. 6,117,949, Rathi et al. disclose A water soluble biodegradable ABA- or BAB-type triblock polymer is disclosed that is made up of a major amount of a hydrophobic polymer made of a poly(lactide-co-glycolide) copolymer or poly(lactide) polymer as the A-blocks and a minor amount of a hydrophilic polyethylene glycol polymer B-block, that possesses reverse thermal gelation properties.
U.S. Pat. No. 5,980,948 describes a composition comprised of a product including a biologically active agent encapsulated in a matrix comprising a polyetherester copolymer, such as a polyethylene glycol terephthalate/polybutylene terephthalate copolymer. The polyetherester copolymer protects the biologically active agent (including proteins, peptides, and small drug molecules) from degradation or denaturation.
U.S. Pat. No. 5,747,058 describes a delivery system in situ which uses sucrose acetate isobutyrate (SAIB). Sucrose acetate isobutyrate is a highly lipophilic sugar derivative, which is currently used as stabiliser and emulsifying agent to human diets in the Food Industry. This technology, called SABER™, was patented by Tipton and Richard (Southern Biosystems, Inc.) in 1995. The high viscosity of the liquid sucrose acetate isobutyrate carrier is lowered by the addition of a water soluble or miscible solvent such as ethanol or dimethylsulfoxide. After addition of the drug, the composition is injected and forms a highly viscous implant in situ, which releases the drug over time.
EP 1184032 describes a method for producing hydrogels, based on crystallization of dextran or derivatives thereof. These hydrogels find use in pharmaceutical, medical and biotechnological applications, e.g. as controlled release systems for the delivery of active ingredients in in vivo and in vitro applications. The hydrogels according to the present invention are priced by crystallization from an aqueous solution that is essentially free of organic solvents or crystallization enhancers.
EP0842657 describes a two phase controlled release system containing dextran and polyethylene glycol. EP0941068 describes a two phase dextran containing controlled release system for proteins.
Many of these and other controlled release formulations are limited by their elevated viscosity, which leads to many delivery difficulties, such as high required hand strength, long delivery times, and pain and fear associated with the large bore needle. Thus, there is a need to deliver these compounds in a rapid, automated fashion without a needle.
Needle-free injectors are available using many different types of energy, and the energy may be supplied by the user, for example where a spring is manually compressed and latched to temporarily store the energy until it is required to “fire” the injector. Alternatively, the injector may be supplied having the energy already stored—for instance by means of a precompressed spring (mechanical or gas), or pyrotechnic charge.
Some injectors are intended for disposal after a single use, whereas others have a re-loadable energy storage means and a disposable medicament cartridge, and there are many combinations to suit particular applications and markets. For the purposes of the present disclosure, the term “actuator” will be used to describe the energy storage and release mechanism, whether or not it is combined with the medicament cartridge. In all cases, it is necessary to arrange for sufficient force at the end of the piston stroke to deliver the entire medicament at the required pressure.
EP 0 063 341 and EP 0 063 342 disclose a needle-free injector which includes a piston pump for expelling the liquid to be injected, which is driven by a motor by means of a pressure agent. The liquid container is mounted laterally to the piston pump. The amount of liquid required for an injection is sucked into the pump chamber by way of an inlet passage and a flap check valve when the piston is retracted. As soon as the piston is moved in the direction of the nozzle body the liquid is urged through the outlet passage to the nozzle and expelled. The piston of the piston pump is a solid round piston.
EP 0 133 471 describes a needle-free vaccination unit which is operated with carbon dioxide under pressure, from a siphon cartridge by way of a special valve.
EP 0 347 190 discloses a vacuum compressed gas injector in which the depth of penetration of the injected drug can be adjusted by means of the gas pressure and the volume of the drug can be adjusted by way of the piston stroke.
EP 0 427 457 discloses a needle-free hypodermic syringe which is operated by means of compressed gas by way of a two-stage valve. The injection agent is disposed in an ampoule which is fitted into a protective casing secured to the injector housing. The ampoule is fitted on to the end of the piston rod. Disposed at the other end of the ampoule is the nozzle whose diameter decreases towards the end of the ampoule.
WO 89/08469 discloses a needle-free injector for one-off use. WO 92/08508 sets forth a needle-free injector which is designed for three injections. The ampoule containing the drug is screwed into one end of the drive unit, with the piston rod being fitted into the open end of the ampoule. At its one end, the ampoule contains the nozzle through which the drug is expelled. A displaceable closure plug is provided approximately at the center of the length of the ampoule. The dose to be injected can be adjusted by changing the depth of the ampoule. The piston rod which projects from the drive unit after actuation of the injector is pushed back by hand. Both units are operated with compressed gas.
WO 93/03779 discloses a needle-free injector with a two-part housing and a liquid container which is fitted laterally to the unit. The drive spring for the piston is stressed by means of a drive motor. The spring is released as soon as the two parts of the housing are displaced relative to each other by pressing the nozzle against the injection location. Respective valves are provided in the intake passage for the liquid and in the outlet of the metering chamber.
WO 95/03844 discloses a further needle-free injector. It includes a liquid-filled cartridge which at one end includes a nozzle through which the liquid is expelled. At the other end the cartridge is closed by a cap-type piston which can be pushed into the cartridge. A piston which is loaded by a pre-stressed spring, after release of the spring, displaces the cap-type piston into the cartridge by a predetermined distance, with the amount of liquid to be injected being expelled in that case. The spring is triggered as soon as the nozzle is pressed sufficiently firmly against the injection location. This injector is intended for one-off or repeated use. The cartridge is arranged in front of the spring-loaded piston and is a fixed component of the injector. The position of the piston of the injector which is intended for a plurality of uses is displaced after each use by a distance in a direction towards the nozzle. The piston and the drive spring cannot be reset. The pre stressing of the spring is initially sufficiently great to expel the entire amount of liquid in the cartridge all at once. The spring can only be stressed again if the injector is dismantled and the drive portion of the injector assembled with a fresh, completely filled cartridge.
U.S. Pat. No. 5,891,086 describes a needle-free injector, combining an actuator and a medicament cartridge. The cartridge is pre-filled with a liquid to be injected in a subject, and having a liquid outlet and a free piston in contact with the liquid, the actuator comprising an impact member urged by a spring and temporarily restrained by a latch means, the impact member being movable in a first direction under the force of the spring to first strike the free piston and then to continue to move the piston in the first direction to expel a dose of liquid through the liquid outlet, the spring providing a built-in energy store and being adapted to move from a higher energy state to a lower energy state, but not vice versa. The actuator may comprise trigger means to operate the said latch, and thus initiate the injection, only when a predetermined contact force is achieved between the liquid outlet of the said cartridge and the subject. Further examples and improvements to this needle-free injector are found in U.S. Pat. Nos. 6,620,135, 6,554,818, 6,415,631, 6,409,032, 6,280,410, 6,258,059, 6,251,091, 6,216,493, 6,179,583, 6,174,304, 6,149,625, 6,135,979, 5,957,886, 5,891,086, and U.S. Pat. No. 5,480,381, incorporated herein by reference.
U.S. Pat. No. 3,859,996, Mizzy, discloses a controlled leak method to ensure that the injector orifice is placed correctly at the required pressure on the subject's skin at the correct normal to the skin attitude. When placement conditions are met, controlled leak is sealed off by contact pressure on the subject's skin, the pressure within the injector control circuit rises until a pressure sensitive pilot valve opens to admit high pressure gas to drive the piston and inject the medicament.
WO Patent 82/02835. Cohen and Ep-A-347190, Finger, discloses a method to improve the seal between the orifice and the skin and prevent relative movement between each. This method is to employ a vacuum device to suck the epidermis directly and firmly onto the discharge orifice. The discharge orifice is positioned normal to the skin surface in order to suck the epidermis into the orifice. This method for injection of the medicament into the skin and the injector mechanism are different and do not apply to the present invention because of its unique ampule design.
U.S. Pat. No. 3,859,996, Mizzy, discloses a pressure sensitive sleeve on the injector which is placed on the subject, whereby operation of the injector is prevented from operating until the correct contact pressure between orifice and the skin is achieved. The basic aim is to stretch the epidermis over the discharge orifice and apply the pressurized medicament at a rate which is higher than the epidermis will deform away from the orifice.
U.S. Pat. No. 5,480,381, T. Weston, discloses a means of pressuring the medicament at a sufficiently high rate to pierce the epidermis before it has time to deform away from the orifice. In addition, the device directly senses that the pressure of the discharge orifice on the subject's epidermis is at a predetermined value to permit operation of the injector. The device is based on a cam and cam follower mechanism for mechanical sequencing, and contains a chamber provided with a liquid outlet for expelling the liquid, and an impact member, to dispell the liquid.
U.S. Pat. No. 5,891,086, T. Weston, describes a needle-free injector that contains a chamber that is pre-filled with a pressurized gas which exerts a constant force on an impact member in order to strike components of a cartridge and expulse a dose of medicament. This device contains an adjustment knob which sets the dose and the impact gap, and uses direct contact pressure sensing to initiate the injection.
A number of biologically-active agents in viscous formulations would benefit from being delivered using the needle-free injector. This group could consist of (but not limited to) anti-inflammatory agents, antibacterial agents, antiparasitic agents, antifungal agents, antiviral agents, anti-neoplastic agents, analgesic agents, anaesthetics, vaccines, central nervous system agents, growth factors, hormones, antihistamines, osteoinductive agents, cardiovascular agents, anti-ulcer agents, bronchodilators, vasodilators, birth control agents and fertility enhancing agents, interferon alpha, growth hormone, osteoporosis drugs including PTH and PTH analogs and fragments, obesity drugs, psychiatric drugs, anti-diabetes, female infertility, AIDS, treatment of growth retardation in children, hepatitis, multiple sclerosis, migraine headaches, and allergic reactions.